Poly(arylene ether) is a type of plastic known for its excellent water resistance, dimensional stability, and inherent flame retardancy. Properties such as strength, stiffness, chemical resistance, and heat resistance can be tailored by blending it with various other plastics in order to meet the requirements of a wide variety of consumer products, including plumbing fixtures, electrical boxes, automotive parts, and coated wire. Poly(arylene ether)s are also used as additives to thermoset resins, which are materials that cure to form very hard plastics. The addition of a poly(arylene ether) can make a cured thermoset resin much less brittle.
For some uses and particularly for use in thermoset compositions, the poly(arylene ether) can be modified by “capping” the terminal hydroxy groups with a polymerizable group such as a methacrylate ester. The capping reactions are associated with reagents, catalysts, and byproducts that can contaminate the resulting capped poly(arylene ether) and detract from the dielectric properties of a thermoset composition into which the capped poly(arylene ether) is incorporated. Some methods for separating capping-related contaminants are known, but they have substantial drawbacks. As described in U.S. Pat. No. 6,897,282 to Freshour et al., precipitating the capped poly(arylene ether) from an antisolvent reduces the level of capping related contaminants relative to a total isolation procedure. However, the capped poly(arylene ether) yields from precipitation are sometimes poor, particularly for low intrinsic viscosity capped poly(arylene ether)s. Furthermore, the precipitation process creates antisolvent handling and disposal problems and also produces a capped poly(arylene ether) with poor solid particle characteristics. The Freshour patent also discloses a method of “washing” (extracting) a capping reaction mixture with water prior to total isolation by devolatilizing extrusion. However, that method requires large volumes of the water wash solution (at least a 1:1 volume/volume ratio of water wash to poly(arylene ether) solution), and the method was ultimately ineffective in that residual levels of impurities in the isolated capped poly(arylene ether) were high (for example, methacrylic acid levels of 2,668 to 25,003 ppm were observed in the isolated capped poly(arylene ether)). Also, the present inventors have observed that the laboratory scale methods in the Freshour patent were difficult to scale to a commercial process. Accordingly, there remains a need for improved methods of isolating capped poly(arylene ether)s. In particular, there is a need for a process that produces a high yield of the capped poly(arylene ether) and substantially reduces the concentrations of capping-related impurities.